In the last couple of days, I've observed a phenomenon I don't remember seeing in years past, perhaps because the city has a different mix of tree species around my new place. It looks like all the silver maples in Ravenswood dropped their leaves just in the past 72 hours:
All the other trees in the neighborhood took their time over the warm, dry fall we've had, but the silver maples hung on like a 6-year-old holding his breath.
Researching this post, I learned that the city requires property owners to limit Norway and silver maples to 5% of the total population of trees they plant. Maples account for 38% of Chicago's trees (as of 2013), so the city recommends planting London planetrees, Chicago Blues black locusts, and Chicagoland hackberries, among a few others.
It shouldn't have surprised me that Chicago itself has become a specific ecological niche with its own local plant species. I can't wait to see rattus norvegicus chicagoensis lurking in my alley...but I'd bet they're out there.